<!--
Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE
The complete set of authors may be found at http://polymer.github.io/AUTHORS
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS
-->
<link rel="import" href="../polymer/polymer.html">

<!--
`core-signals` provides basic publish-subscribe functionality.

Note: avoid using `core-signals` whenever you can use
a controller (parent element) to mediate communication
instead.

To send a signal, fire a custom event of type `core-signal`, with
a detail object containing `name` and `data` fields.

    this.fire('core-signal', {name: 'hello', data: null});
    
To receive a signal, listen for `core-signal-<name>` event on a 
`core-signal` element.

  <core-signal on-core-signal-hello="{{helloSignal}}">

You can fire a signal event from anywhere, and all 
`core-signal` elements will receive the event, regardless
of where they are in DOM.

@group Polymer Core Elements
@element core-signals
@status stable
@homepage github.io
-->
<polymer-element name="core-signals">
<script>
(function(){
  
  Polymer({
    attached: function() {
      signals.push(this);
    },
    removed: function() {
      var i = signals.indexOf(this);
      if (i >= 0) {
        signals.splice(i, 1);
      }
    }
  });

  // private shared database
  var signals = [];

  // signal dispatcher
  function notify(name, data) {
    // convert generic-signal event to named-signal event
    var signal = new CustomEvent('core-signal-' + name, {
      // if signals bubble, it's easy to get confusing duplicates
      // (1) listen on a container on behalf of local child
      // (2) some deep child ignores the event and it bubbles 
      //     up to said container
      // (3) local child event bubbles up to container
      // also, for performance, we avoid signals flying up the
      // tree from all over the place
      bubbles: false,
      detail: data
    });
    // dispatch named-signal to all 'signals' instances,
    // only interested listeners will react
    signals.forEach(function(s) {
      s.dispatchEvent(signal);
    });
  }

  // signal listener at document
  document.addEventListener('core-signal', function(e) {
    notify(e.detail.name, e.detail.data);
  });
  
})();
</script>
</polymer-element>
